Studies on the biosynthesis of basement membrane in vivo and in vitro using autoradiography with electron microscopy will be completed. Studies of degradation of basement membrane utilizing the newly discovered enzymes in involuting breast will be continued. The enzyme will be purified, characterized, and the degraded product of the basement membrane hydrolyzed by this enzyme will be characterized. Its role, if any, in invasiveness of tumors will be studied. Further modifications of the enzyme-labeled technique are required to obtain better fixation of tissue and preservation of antigens. BIBLIOGRAPHIC REFERENCES: Martinez-Hernandez, A., Nakane, P. K. and Pierce, G.B. Intracellular localization of basement membrane antigen in parietal yolk sac cells. Amer. J. Path. 76: 549-560, 1974. Pierce, G. B., Nakane, P. K. and Mazurkiewicz, J. E. Natural History of Malignant Stem Cells. Proceedings of the 4th International Symposium of the Princess Takamatsu Cancer Research Fund, Tokyo, 1973. "Differentiation and Control of Malignancy of Tumor Cells," W. Nakahara, T. Ono, T. Sugimura and H. Sugano, eds., University of Tokyo Press, Tokyo, Japan, 1974, pp. 453-469.